The present invention relates generally to connectors used in connections with signal cables, especially high-speed signal cables, and printed circuit boards and more particularly to high density connectors of modular construction which have selected impedances.
Many electronic devices rely upon transmission lines to transmit signals between related devices or between peripheral devices and circuit boards of a computer. These transmission lines incorporate signal cables that are capable of high-speed data transmissions.
These signal cables may use one or more twisted pairs of wires that are twisted together along the length of the cable, and each such pair being encircled by an associated grounding shield. One wire of the pair may see a +1.0 volt signal, and the other wire of the pair may see a −1.0 volt signal and thus, these wires are called “differential” pairs, a term that refers to the differential, i.e., opposing and balanced signals they carry. Such a twisted pair construction minimizes or diminishes any induced electrical fields form other electronic devices and thereby eliminates electromagnetic interference.
In order to maintain electrical performance integrity from such a transmission line, or cable, to the circuitry of an associated electronic device, it is desirable to obtain a substantially constant impedance throughout the transmission line and to avoid large discontinuities in the impedance of the transmission line. The difficulty of controlling the impedance of a transmission line connector at a connector mating face is well known because the impedance of a conventional connector typically changes through the connector and across the interface of the two mating connector components, particularly with high-density connectors. Although it is relatively easy to maintain a desired impedance through an electrical transmission line, such as a cable, by maintaining a specific geometry or physical arrangement of the signal conductors and the grounding shield, an impedance change is usually encountered in the area where a cable is mated to a connector. If this impedance change is great, it effects the integrity of the signals transmitted across the transmission line. It is therefore desirable to maintain a desired impedance throughout connector interfaces, including their connection to cables and circuit boards.
As shown in U.S. Pat. No. 6,280,209, issued Aug. 28, 2001, it is known that the impedance of a connector system may be selected, or “tuned” when arranging the ground terminal and a pair of associated differential signal terminals in a triangular orientation to form a triplet arrangement of terminals. However, this structure does not address the issue of how to increase the density of terminals within such a connector.
The present invention is therefore directed to a termination structure for providing improved, high-density connections between cables and connectors that provide a high level of performance and which maintains the electrical characteristics of the cable through the mating interface between the cable and device connector in the termination area.